In wireless communication systems based on Code Division Multiple Access (CDMA), there is a need to integrate real-time circuit switched services, such as voice services, and non-real time best-effort packet data services on a same frequency carrier. An extensive amount of work has been done to design systems that are optimized to support either real-time circuit switched services or non-real time best-effort packet data services. Currently, for most efficient resource utilization, the different services are provided on separate frequency carriers. However, providing the different services on separate frequency carriers makes it difficult to support simultaneous real-time circuit switched and non-real time best-effort pack data services for a same user. The obstacle preventing both types of services from being efficiently provided via a same frequency carrier is the limited amount of available transmit power per base station, as will be described herein.
FIG. 4 depicts a wireless communication system 10 employing CDMA techniques. The wireless communications system 10 comprises a mobile switching center (MSC) 12 and a plurality of base stations (BS) 14-i connected to the MSC 12. Each of BS 14-i has a maximum amount of available power Pmax for forward link or downlink transmissions to mobile-telephones (MT), such as mobile-telephones 16-k, within an associated geographical coverage area referred to herein as cell 18-i. For illustrative purposes, cells 18-i are depicted as circular in shape with base stations 14-i centrally positioned. It should be understood that cells 18-i may also be noncircular in shape (e.g., hexagonal) with the base stations positioned non-centrally.
Second generation CDMA based wireless communication systems were optimized to support voice services. The systems utilize frame delivery over dedicated channels (or in other words, real-time circuit switched services) with very low delay and jitter to support voice services. In second generation CDMA based wireless communication systems, the forward link comprises a plurality of signals which have been combined and modulated onto a frequency carrier, wherein the plurality of signals includes a pilot signal, control signals and voice signals. The pilot and control signals are transmitted over a pilot channel and control channels defined by Walsh codes Wpilot and Wcontrol-cc at fixed transmit powers Ppilot and Pcontrol-cc, respectively, wherein Ppilot and Pcontrol-cc are fixed percentages of Pmax and “cc” denotes a specific control channel. Note that the pilot channel is always active because, in second generation CDMA systems, the pilot signal is a continuous pilot signal. By contrast, the control channels are not always active.
The voice signals are transmitted over traffic channels defined by Walsh codes Wvoice-tc at transmit power Pvoice-tc, where “tc” denotes a specific traffic channel. The transmit power Pvoice-tc of the voice signals are dynamically power controlled based on users to which the associated voice signals are intended.
The fundamental objective of power control is to set the voice transmit power Pvoice-tc such that a desired quality of service (QOS) is obtained at a receiver for the associated voice signal. Power control comprises of outer and inner power control loops. Outer power control loops involve, for each traffic channel, setting a target signal-to-interference ratio (SIR) or other target control threshold that will achieve a desired frame error rate (FER) or other QOS parameter at the intended receiver for the voice signal. By contrast, inner power control loops involve, for each traffic channel, manipulating transmit power at the transmitter according to the target SIR set by the outer power control loop. Specifically, the inner power control loop measures SIR at the receiver over a time interval referred to herein as a power control group (PCG). If the measured SIR is greater than the target SIR, the receiver transmits power control bits on the reverse link or uplink indicating to the transmitter to increase its transmit power an up transmit step size. By contrast, if the measured SIR is less than the target SIR, the receiver transmits power control bits indicating to the transmitter to decrease its transmit power a down transmit step size. This manipulation of power ensures that the SIR at the receiver is at or near the target SIR in order to achieve the desired QOS at the receiver. Note that power control may also be applied to signals other than voice.
FIG. 5 depicts a chart 19 illustrating forward link transmit power Pfl versus time at BS 14-i for a forward link comprising pilot, control and voice signals, wherein forward link transmit power Pfl is the sum of the transmit powers of the signals comprising the forward link, i.e., Pfl=ΣPpilot+Pcontrol-cc+Pvoice-tc. Note that the pilot transmit power Ppilot is fixed because the pilot signal is continuously being transmitted over the pilot channel at a fixed transmit power. By contrast, the combined control and voice transmit powers Pcontrol-cc and Pvoice-tc is variable for a number of reasons: the control and traffic channels are not always active; the traffic channels are dynamically power controlled; and traffic channels are being added and dropped as calls to mobile-telephones are being completed and terminated. The forward link transmit power Pfl preferably should not exceed the maximum transmit power at BS 14-i otherwise calls may be dropped due to a number of reasons, such as degradation in quality.
In third generation CDMA based wireless communication systems, data services have been added. Data services differ from voice services in a number of manners. Voice services utilize real-time circuit-switched services in which channels are dedicated. Real-time circuit switch services involve frame delivery with very low delay and jitter. Typically, retransmissions are not allowed and the quality of voice signal transmissions are controlled very tightly through dynamic power control. By contrast, data services utilizes best-effort, non-real time packet data services which do not place stringent requirements on delay and jitter. Data signals are transmitted using time-slotted transmissions on shared channels. Retransmissions are utilized to achieve extremely reliable data delivery while compensating for instantaneous physical layer losses due to fading.
There are currently two manners of implementing data services with voice services. The first proposal has been incorporated into the well known third generation CDMA standard (hereinafter referred to as 3G-1x), and involves providing data services using a same frequency carrier as the one on which the voice services are provided. The second proposal has been incorporated into the well known data only evolution of the third generation CDMA standard (hereinafter referred to as 3G-1x EVDO), and involves providing data services using a different frequency carrier than the frequency carrier on which the voice services are provided.
Both 3G-1x and 3G-1x EVDO utilize measured SIR at the receivers or mobile-telephones 16-k to control a parameter associated with the transmission of data from BS 14-i. Specifically, in 3G-1x, data is transmitted at fixed data rates utilizing measured SIR to control transmit power levels and, in 3G-1x EVDO, data is transmitted at fixed transmit power levels utilizing measured SIR to control data rates. Thus, data services in 3G-1x is similar to voice services in that both services are power controlled, whereas data services in 3G-1x EVDO is “rate controlled.”
In 3G-1x, voice and data services are provided using a same frequency carrier. That is, the voice and data signals are parts of a single forward link, wherein the data signals are transmitted over data channels defined by Walsh codes in the forward link at transmit power Pdata-dc and “dc” denotes a specific data channel. Data is transmitted over dynamically power controlled data channels at fixed data rates such that the forward link has an associated SIR at the receiver which is at or near a target SIR. Without decreasing the number of available voice channels at BS 14-i, the addition of data channels at BS 14-i can cause the forward link transmit power Pfl to, at times, exceed the maximum transmit power Pmax at BS 14-i due to the dynamics of power control. See FIG. 6, which depicts a chart 20 illustrating forward link transmit power Pfl versus time at BS 14-i for a forward link comprising pilot, control, voice and data signals, i.e., Pfl=ΣPpilot+Pcontrol-cc+Pvoice-tc+Pdata-dc.
In 3G-1x EVDO, voice and data services are provided using separate frequency carriers. That is, the voice and data signals are transmitted over separate forward links defined by different frequency carriers. Data is transmitted over data channels at fixed data transmit powers Pdata-dc but at variable data rates. Specifically, measured SIR at the receiver is used to determine a data rate which can be supported by the receiver. Typically, the determined data rate corresponds to a maximum data rate at which a minimum level of quality of service can be achieved at the mobile-telephone. Higher measured SIR translates into higher data rates, wherein higher data rates involve higher order modulation and weaker coding than lower data rates. For example, if measured SIR at the receiver is 12 dB and −2 dB at two different receivers, then the data rates may be 2.4 mbs and 38.4 kbs at each of the respective receivers. See FIG. 7, which depicts a chart 30 illustrating forward link transmit power Pfl versus time at BS 14-i over a data only frequency carrier, where Pfl=ΣPdata-dc.
However, the use of different frequency channels for voice and data services makes it difficult to support simultaneous real-time circuit switched services and non-real time best-effort packet data services for a same user. Significant changes to network architecture would be required. Accordingly, there exist a need to integrate voice and data services onto a same frequency channel.